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Full text of "How_RAID_Works_"

RAID Presentation 



Raid is an acronym for "Redundant array of 
independent Drives", or Redundant array of 
inexpensive drives". The main concept of 
RAID is the ability to take multiple drivers 
and combine them together. 

Another type of RAID is RAID 5 



How RAID works 



Raid is used to take multiple drives and 
have them virtualized as a single driver. All 
Raid structures contain one of two primary 
purposes: aggregated storage space or data 
redundancy. Both regular RAID and RAID 
5 work the same way but what they can do 
is different. 



How RAID 5 works 

Raid 5 provides a very redundant fault 
tolerance in addition to performance 
advantages allowing data to be safeguarded. 
Raid 5 requires at least 3 120gb hard drives, 
you will have 240gb of actual usable space. 
The more drives you use then the more 
efficient your storage space becomes. If you 
had five 120gb hard drives, you would have 
480gb of usable space. 



Data redundancy 

Your data can survive a complete failure of 
one hard drives, but if two drives fail at the 
same time, ALL data will be lost. Raid 5 
array can actually still be used with one 
drive completely missing or not working. 
The data will then be rebuild on the fly. 
Recommended that you have a extra hard 
drive by your computer if this ever 
happens. 



RAID 5 



Raid 5 has a increased over head. This is the 
cost to the person for the extra hard drive 
that is taken up by the parity. If you have 
two hard drives and you want to have that 
much space available, you need to buy one 
more hard drive for parity. 



Striping parity 

Data is "striped" across the hard drives, 
with a dedicated parity block for each 
stripe. A, B, C and D represent data 
"stripes". Each stripe vary in size from 4kb 
to 256kb per stripe. Stripes with a subscript 
P are the parity blocks. The parity is 
responsible for the data fault tolerance and 
is also the reason why you lose the amount 
of space equivalent to one drive 



Striping parity 



Lets say the second hard 
drive fails. When the new 
one is put in place the 
RAID controller would 
rebuild the data 
automatically. The data 
segments Al and A3 
would rebuild A2. Parity 
blocks are determined by 
using a logical comparison 
called XOR. 




DiskO 



RAID 5 




Disk 1 




Disk 2 




Disk 3 



RAID performance 

Raid 5, stores one file in three different hard 
drives. It then can be accessed in 1/3 the time. 
Because it will be read from all three drives. Each 
hard drive stores 1/3 of the file. This in a perfect 
situation, causes your read speed to be tripled - 
with even more performance potential in RAID 5 
arrays containing additional hard drives. THE 
downfall is there is an increased overhead when 
writing to the drives caused by parity calculations. 



RAID 10 



RAID has levels 0-9, but you can add two single 
digit numbers to create a 2 digit number like 
RAID 1+0 to get Raid 10. Raid 10's advantages 
are its very fast, it's crash proof, and it eats disk 
space.For Raid 10 you need at least 2 physical 
hard drives. You also need a disk controller that's 
understands RAID. Raid 10 works by striping and 
mirroring your data across at least two disks. 
Mirroring, or RAID 1 , means writing your data to 
two or more disks at the same time. 



RAID 10 



If one disk fails then completely, then the mirror 
preserves the information. Raid is stripping 
which allows the data to be broken up and written 
to different hard drives. This improves the 
performance because the computer gets data from 
more than one disk at the same time. Raid in not 
really a raid level because it doesn't provide any 
redundancy to protect information. Its still 
considered a raid level. 



B ack up and Raid 1 



Although the data is written on to two disks, the 
data is not being backed up. If your system fails, 
rather then the disk, suffer an error an enormous 
amount of data could be sent to both disks at the 
same time, which would corrupt both drives. If 
using RAID 1 then you should still have a back 
strategy in place, but putting raid and raid 1 
together and getting raid 10 secures the data better 
because mirroring duplicates all your data. It's fast 
because data is striped across two or more disks at 
the same time. 



Disadvantages of RAID 10 

The disadvantages of having RAID 10 is that it 
cuts your effective disk space in half. Since all 
data is mirrored, two 60 GB disks give you a total 
system capacity of 60 GB. And you should use 
identical disks when creating a mirrored array. 
Raid 10 is also slightly more complex to set up 
than conventional storage. It usually takes about 
10 minutes to install raid on your computer. If the 
disk controller on your mother board doesn't 
support Raid 10 then you can get an add-in disk 
controller card. 



History of raid 



David A. Patterson led a team at the university of 
California, Berkeley that developed the idea of 
RAID storage. In 1987 Patterson said "We had just 
been working on RISC processors, and we 
consciously said, Processors are going to start 
getting fast, improving faster than they have in the 
past". Patterson then had the graduate students 
think about ideas that were involved with the 
processes of making Processors faster. 



History of RAID 

1956 - IBM officially announces the RAM AC 
305, the first hard disk system, which holds 5MB 
of data. 

1961 - Ampex develops helical scanning video 
recording, which well later be adapted for high- 
capacity tape backup. 

1962 - IBM Advanced disk file used one head for 
each disk surface, which eliminates the need for 
compressed air to position heads. 

1973 - IBM's hermetically sealed Winchester hard 
disks become the standard design for disk drives. 



History of RAID 



1979 - Philips demonstrates optical storage drive 
technology as part of a joint venture with control 
data corp. 

1988 - David A. Patterson leads a team that 
defines RAID standards for improved 
performance, reliability. 

1995 - EMC develops the concept of network- 
attached storage 

1998 - Gigabit Ethernet becomes a formal IEEE 
standard. 



History of raid 

Raid 5 was released in 1995, on June 8. 
Raid was released on march 5, 2004 
Raid 1 was released on June 5, 2007 
Raid 10 was released on June 7, 2007 



Different type of RAID 



• RAID 6 


RAID 53 


• RAID 5 


RAID 0+1 


• RAID 4 


RAID-s 


• RAID 3 


RAID 50 


• RAID 2 


RAIDZ 


• RAID 1 




• RAIDO 




• RAID 7 




• RAID 1+0 





Manufactures 

Promise technology Inc 

3 ware inc 

Ciprico inc 

RAIDmax 

Arco Computer products, inc 

Bering technology inc, 

Chih Kang Material Co 

Casepro technology Co 



Control cards $ 



PCI Express S ATA / IDE combo controller card - 
$21.99 

Areca ARC- 1236 1ML-2G PCI- Express X8 SATA 
2 controller Card - $899.99 

Highpoint Raocketraid 43 1 PCI- Express x8 
Four-port SATA and SAS hardware - $229.99 

Highpoint Raocketraid 2640X4 PCI-Express x4 
Four-port SATA and SAS RAID - $99.99 



References 



http://www.lascon. co.uk/d008005. htm 

http://www.newegg.com/store/SubCateg 
ory.aspx?SubCategory=410&Tpk=RAID 
%20cards 

http://www.computerworld.eom/s/article/ 
87093/The_Story_So_Far 

http://www.scottklarr.com/topic/23/how-